For optical signal transmission over an optical fiber system, there is a need to monitor the optical power in and out of optical devices or an optical system such as fiber amplifier and variable attenuator. A common method employed in conventional fiber optical system is to connect a tap optical coupler to the input end or/and the output end of the fiber pigtail of the devices or the system. A small amount of light power is directed from the input or output as a reference to monitor the input or/and output optical power. Such approach however suffers several drawbacks. The size of the sign transmission is increased when one more optical element is added. Stability of optical signal transmission and tapped output measurement may be degraded if the coupling between the tap coupler to the collimator is not properly connected. Signal power loss may also occur due the requirement of transmitting the signal through the tap optical coupler as an additional optical element. The simplest way to solve the problem is to use taped optical collimator to assemble the device that has built-in tap collimator to direct a portion power from input or/and output side. The tap-input collimator is commercially available. It is made by a dual fiber collimator in that two fibers are placed side by side in parallel in a glass capillary and share a same collimator lens, preferably the GRIN lens. When an input light is coupled into one fiber of such input tap collimator, since the fiber Is positioned in the dual core glass capillary and the fiber core is off-axis of the GRIN lens, the collimated beam has a declined angle against the axis of GRIN lens. A part of the beam is reflected from the far-end of GRIN lens surface or from a partial reflector glued on the GRIN lens surface. The reflected part of the beam receives a equal opposite decline angle from the reflector and is focused by the same GRIN lens to another finer in the glass capillary. The second fiber is the tap fiber carrying the tap power. The main portion of the light pass through the partial reflection glass piece to provide ongoing collimated beam.
However, the tap-output collimator is not yet made available mainly because of difficulties to divide incoming light beam into two beams in proper ration with opposite declined angle to project two beams into two fibers in a dual fiber glass capillary respectively.
For these reasons, there is a need in the art of optical fiber signal transmission to provide a new and improved apparatus and method for tapping out a small portion of received signal power from a collimator for measuring and monitoring the optical signal transmission. Preferably, the new and improved configurations and methods are simple and easy to implement with compact configuration for low cost production.